Implantable and insertable medical devices are commonly used in the body at various locations. Implantable medical devices are described as those that are delivered to a target site in the body and designed to reside at that site for a period of time to affect treatment of an individual. Examples of these implantable devices include prosthetic devices such as stents. Insertable medical devices refer to those in which a portion or the entire device is introduced into the body, but that are not necessarily required to reside at the target location in the body for an extended period of time. Insertable medical devices can include those that are moved in the body, such as to deliver a fluid, drug, or an implantable medical device to a target location in the body. Examples of insertable devices include catheters, endoscopes, cystoscopes, guidewires, needles, trocars, and the like.
Many implantable or insertable medical devices are used in processes where they are moved against body tissue. For example, these devices are often moved against the lining of a body lumen, such as one in the cardiovascular system (e.g., an artery or vein), or one in the urogenital system, such as the urethra, or fallopian tube. As a general matter, it is desirable to provide a device surface that minimizes trauma to tissue that it is moved against.
However, implantable or insertable medical devices are typically fabricated from biocompatible metals or certain plastic materials that inherently do not possess a low friction or lubricious surface. To address this, lubricants and coatings have been used to reduce the frictional forces that facilitate movement of the device in relation to body tissue.
One approach to providing a lubricious surface on implantable or insertable medical devices has been to immobilize a hydrophilic polymer such as poly(ethylene glycol), poly(acrylamide,) or poly(vinylpyrrolidone) on the surface of the device. These polymers attract water, and become slick upon hydration, resulting in a device surface that has “wet” lubricity. However, these types of coatings can swell substantially and increase the coating thickness when hydrated. Also, since lubricity relies on these being substantially hydrated, lubricity can be lost if water is squeezed out of the coating.
Rather than using a hydrophilic “wet” low friction coating, the medical device may be fabricated from using a material such as polytetrafluoroethylene (PTFE) which can provide a low friction “dry” surface. PTFE is well-known for its chemical resistance, high temperature stability, resistance against ultra-violet radiation, low friction coefficient and low dielectric constant, among other properties. As a result, it has found numerous applications in harsh physico-chemical environments and other demanding conditions. For example, in some cases, one approach has been to provide a polytetrafluoroethylene (PTFE) coating, which provides a “dry lubricity” to the device surface. Although the PTFE displays excellent low frictional properties, it can be very difficult to make coatings or portions of devices from PTFE because of its high melting point. In addition, PTFE repels water, and although low friction, the lubricity is not enhanced when contacted with water which is present in body fluid in contact with a device surface.
Applicants have found that it would be highly desirable to provide coatings that have both properties of dry and wet lubricity, and that also display one or more properties such as biocompatibility, durability, and compliance. The novel fluoropolymer and fluoropolymer-containing compositions disclosed herein provide these features and represent distinct improvements in the art of low friction coatings for medical devices.